During last night's mayoral debate, the candidates reportedly agreed to release their tax returns. This arose from the fact that Ken Livingstone is suspected of keeping his taxes arranged in an exotic manner, so Boris Johnson and Conservatives in Parliament attacked Livingstone for his tax affairs, and therefore Ken began to question Boris' own arrangements. The day before last night's debate, Boris told Ken "You've got to stop lying" about his taxes, and the culmination of all these allegations is that all four candidates released their tax returns today, as ageed during the debate. Ken had a little more difficulty than the others, but that's a different issue to the one I wish to address.

Earlier this afternoon, the Independent on Sunday's John Rentoul tweeted: "That Americanisation was quite sudden. London mayoral politics now requires the publication of candidates' personal tax returns."

This is a very disappointing situation. I have two gut reactions to the idea that British politicians – one assumes all Parliamentary candidates may now have to do this in future – should release their tax returns. The first is that if we want Parliamentarians of the Carswell school – patriotic people who have decided to enter Parliament not for fame (Today programme fame, anyway), career advancement, or to cash in, we will quickly find the incentives for them to do so are running out. Not only will they endure the general distrust towards MPs as is currently the case, but in future they will be expected to undergo the public trial of having their tax returns released and examined by the local or national press. This is made more important by my second point.

In America, where candidates regularly release their tax returns, there is no great question of a divide in the wealth of candidates. That is to say, both candidates are likely to be millionaires, therefore the real reason for seeing their tax returns is to ensure they have clean records of handling their own affairs. They might use clever lawyers to pay a bit less tax than their opponent, or they might be making money from some sort of insider-y schemes that indicate corruption. Both of these would raise questions about the candidate.

In Britain, however, both/all three major party candidates are not usually millionaires. Often one major candidate is. Indeed, in many seats there will be a stark contrast. One might have a Tory candidate, who, at the age of 45, has run a successful business for the best part of twenty years, and finds himself earning a well-deserved six or seven-figure sum every year. His Labour opponent is a 45 year-old trade union officer. One can imagine how many campaigns, especially in marginal seats, would be dominated purely by news of one candidate being much wealthier than the other.

What would local associations and constituency Labour parties be motivated to do, if all candidates had to disclose tax returns? They would choose candidates who have not been successful in their previous careers. I am very keen for more working class MPs to enter Parliament, and have a greater voice at the top of the Party, but scaring the well-off out of politics, a very possible side-effect, does not seem fair or reasonable. There is no suggestion that those who are successful in business are intrinsically less able to formulate policies to benefit everyone in society, but making candidates disclose their tax returns will soon cause a witch-hunt for wealthy candidates every general election. We should discourage it.